For the first one, I don't think it's wrong, but it's very wordy and unnatural. It would be better to say: - I've finished the work that I was supposed to do. - I've done everything that I am supposed to have done. - I've done what I needed to do. I'm not entirely sure what you mean by "The kindergarten was still working? Perhaps: - The kindergarten class was still going on? (The class was still being taught at that point in time) The other two are fine.

All of those sentences are correct except for the kindergarten was still working. It's better to say, the kindergarten was still open or the staff at the kindergarten was still working. I hope that answers your question. If you'd like to practice speaking, I'd be happy to help you develop a study plan. Feel free to look at my teaching profile and class offerings and send me a message if you think I can help you."